Hallicrafters T-67 HV corona ring

[dcl0]

Well, I had to change all the electrolytics and the paper caps (I tested them as I removed them, they were all leaky). I checked all the resistors and replaced those that were out of spec (one was burnt and broken in half!). I checked and rechecked node by node against the schematic (I had to do some rewiring around the horizontal output tube to put it back to spec). So for the 4th I decided to fire up the T-67 for the first time. No fireworks! But as you can see from the pictures, I have a few problems.

1) When I'm injecting the cross-hair pattern from the VA62 into any channel, I see two vertical lines, not one (I believe the vertical line in the center is the correct one from the test pattern, and the one on the left is an artifact). I see this left hand vertical line on all channels even when no signal is being applied and there is just snow. With the cross hatch pattern the situation is the same. I've adjusted the horizontal and vertical hold as best as I can, and it seems to lock. However the horizontal width and horizontal linearity controls do nothing. I haven't done any alignment or adjustment of the sound trap yet. Does anyone have suggestions as to what might be causing this vertical line?

2) In the cross hair test pattern, I see faint vertical bands on the right half of the screen. Is this 4.5 MHz sound bleeding through?

3) There seems to be black lines between each horizontal scan line-the vertical resolution is bad. Is this normal for this set?

4) The vertical lines seem to be fainter than the horizontal ones. What might be causing this?

I would be grateful for any suggestions you have.

[old_tv_nut]

How about putting a regular picture in instead of a test pattern. Some of the stuff you see could be occurring during retrace, or due to wrong sweep frequencies; hard to identify with a cross-hatch test pattern but easy to see with a normal image, as you could identify part of it folding over.

[old_tv_nut]

Vertical lines fainter than horizontal could just be poor frequency response, could be as simple as fine tuning. Should not worry about this until you are sure you have a stable picture with correct sweep frequencies.

[dcl0]

Fantastic! a real picture is better. Still a bright vertical line though.

[old_tv_nut]

Note the parts of the picture to the left and right of the bright line don't match. this would indicate the horizontal scan is stopping there for a short time. So, you need to look at the horizontal drive and the damper circuit.

Not sure, but I would try adjustment (B1, B4) or replace damper tube.

[Yamamaya42]

Originally Posted by old_tv_nut

Note the parts of the picture to the left and right of the bright line don't match. this would indicate the horizontal scan is stopping there for a short time. So, you need to look at the horizontal drive and the damper circuit.

Not sure, but I would try adjustment (B1, B4) or replace damper tube.

i noticed the same thing, it's a bit weird.

[dcl0]

Hi guys,

I swapped the damper with another NOS tube I had - unfortunately it made no difference. Turning B1 (horizontal drive) crowds the image to the right (as it should) but does nothing with the bright vertical line. Turning B4 (horizontal linearity) does nothing when it is turned (neither does B3, the width).

I poked around with a scope looking first at the control grid of the horizontal output tube V19. Not the best saw-tooth pattern with bumps at the beginning. The pp voltage there is actually 111 volts (I had the wrong probe setting on that one).


Next I looked at pin 2 of the horizontal oscillator V18B which feeds the control grid of V19.


However pin 5 of the horizontal oscillator V18A was difficult to get the scope to trigger on. Ultimately with tweaking of the contrast control I got a stable trace. This section feeds the horizontal linearity and width controls.


Finally looking at the control grid of V18A (pin 4) which collects signal from one side of the horizontal sync discriminator V17 (6AL5). This seems weak with a peak height of only 306 mV. Sams or Riders don't give sample scope images for this set. Do these images seem reasonable?????


As I was rechecking around the horizontal sweep section I noticed something funny. The components wired to pins 2 and 7 on the Horizontal sync discriminator V17 (6AL5) are swapped from what is pictured in the SAMS. However the wiring as found is consistent with what is pictured in Riders. Does this matter? or should K1 be paired with P1 and K2 with P2 for correct function of the tube?

[old_tv_nut]

V18A pin 4 should be mostly DC, with most of the pulses filtered out, so that's OK. When the horizontal is out of sync, you would expect to see a beat note in this filtered discriminator voltage.

The 6AL5 must be wired correctly, or the horizontal wouldn't sync, so SAMS is wrong.

It's troublesome that the width and lin coils have no effect. Maybe you should check if either of them are open or if the connection to pin 5 or 6 of the flyback is open.

[dcl0]

Success! At least with regard to the bright white vertical line. Turns out it was the horizontal drive set too high. According to Grob (page 393 in Basic Televison: Principles & Servicing 1954), you adjust the drive control until the white line or wrinkle appears, then back off enough to eliminate the distortion - it works!....But still no response out of the width or horizontal linearity control. I've checked the resistance from pin 6 to pin 4 of the flyback and I get 9.8 ohms; the horizontal linearity control is 24 ohms. I'll have to disconnect the wire from pin 5 to check the width control. However, I can live with it as is...

One thing I'm wondering about is the slight vertical wavy distortion just to the right of center.

[old_tv_nut]

You checked the flyback winding resistance and the linearity coil resistance, OK. But did you check from the width coil to the flyback to make sure there is a connection?

[dcl0]

I disconnected the lead from pin 5 of the flyback and I'm reading 0.4 ohm from pin 6 to the lead I disconnected from pin 5. When I reconnect the lead to pin 5 and measure from pin 5 to pin 6, I read 0.2 ohms (Both the width coil and a portion of the flyback from pin 5 to 6 are in parallel - for this measurement all the other plugs are disconnected from the power unit to the rest of the TV). It sure seems like I've got continuity through the coils. I've also checked from pins 4,5 and 6 of the flyback to ground and see no shorts. One thing I've noticed is that someone has tried to solder the clip that holds the width coil to the chassis and that solder blob is broken and the coil wiggles in the hole. Does the ferrite (?) core of the coil need to have a good ground for the coil to work properly? I've also checked the back end of the core to see that it rotates and it moves as I rotate the adjustment screw. The same holds for the linearity coil.

[old_tv_nut]

I can't think of a reason that the core would have to be grounded.

Still very strange that adjusting the coils has no effect.
Have you checked the SAMS resistance readings from the pins of V20 and V21?

[dcl0]

I've measured the resistances of V20, starting at pin 1 and relative to chassis: inf, 0, (from pin 8 of V20), inf, 8 kohm, inf, 8 kohm, inf and 0. Interesting that pins 4 and 6 have much greater resistance than specified in SAMS (65 ohm). All pins of V21 read infinity relative to ground. Also one thing I've noticed is that if I back off even more on the horizontal drive a little more, the faint vertical bands just to the right of center disappear. Unfortunately if I back off to the limit of the drive capacitor I still don't get any response from the width or horizontal linearity control. I'm wondering what should the peak to peak voltage of the drive signal to pin 5 of the horizontal output tube be?

[old_tv_nut]

I've run out of ideas for now.

[nasadowsk]

I'd look at those lin and width coils and see if you have any of the mods shown in the Sams. And check those resistors.

I'm also going to toss this out:

Are the yoke and flyback the original ones? I've seen cases where folks sub them and all hell breaks loose...